This invention relates to an apparatus for and a method of smoothing the surface of a substrate such as a magnetic disk substrate.
A magnetic disk substrate serving as a magnetic memory medium is generally produced by forming a NiP layer on the surface of an aluminum or glass substrate, carrying out a texturing process to form a concentrically circular texturing marks on the surface of this NiP layer, thereafter forming a magnetic layer thereon by a sputtering process or the like and then further forming a lubricating protective membrane. According to such a prior art method of production, abnormal protrusions appear on the disk surface in the final stage and such abnormal protrusions are likely to hit the magnetic head, thereby damaging the magnetic disk surface or to cause foreign objects to become attached to the magnetic head. Debris particles thus generated during the production process are also likely to become attached to the disk surface.
In order to remove such abnormal protrusions and debris particles, it has been customary to carry out a surface smoothing process. Japanese Patent Publication Tokko 2-10486, for example, disclosed a smoothing process for the surface of a disk substrate by using a polishing tape with a polishing layer formed thereon and causing it to run while using a rubber roller or the like to apply a pressure for removing the abnormal protrusions on the surface. A smoothing method by running a polishing tape while blowing air from behind the polishing tape, instead of using a roller, has also been practiced. Japanese Patent Publication Tokkai 2001-162504 disclosed another smoothing process by pressing a polishing tape onto the surface of the disk substrate by means of a pad while the disk substrate is caused to rotate and the pad is moved reciprocatingly in a radial direction of the substrate.
The smoothing process carried out while a polishing tape is pressed by means of a rubber roller is effective from the point of view of removing the abnormal protrusions from the surface but is not capable of either preventing the generation of debris particles or removing them since the polishing tape and the rubber roller interfere each other during the polishing process. The method with air is capable of preventing the generation of debris particles because there is no interference such as between a rubber roller and the polishing tape but tends to bring in the debris particles from the surrounding areas because of the air movement. The method of using a pad to press the polishing tape is effective not only in removing debris particles but also in preventing their generation because the polishing tape is not caused to run at the time of polishing, unlike the method using a rubber roller, but there is an interference between the edges of the polishing tape and the pad even while the polishing tape is not running. Moreover, the polishing tape and the pad interfere with respect to each other when the polishing tape is run without contacting the disk substrate for the preparation of a next polishing process. Thus, there is a limit to how much the generation of debris particles due to the falling of abrading particles can be prevented.